How it Works
Philips
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PM 5326
User Manual
138 pgs5.99 Mb2
Service manual
72 pgs73.78 Mb2

Philips Pm5326 User Manual

RF
signal generator
lnst ruction manual
9499
520 08002
Qservice ----- This Document is a complete scan from the Original Tektronix Manual ----- Qservice
CONTENTS
GENERAL
l ntroduction Technical data Accessories
Operating principle
INSTALLATION
Safety regulations
Mounting
Earthing Dismantling the instrument Mains connection
OPERATING INSTRUCTION
Controls and sockets Operation and application Application examples
SERVICE PART
Circuit description
Access to parts Check and adjustment Check after repair and maintenance Parts list
LIST OF FIGURES
Block diagram, complete Front view Amplitude modulation Frequency modulation, adjustment of carrier frequency Wobbling with adjustable frequency marker, adjustment of centre frequency Wobbling with adjustable frequency marker spectrum External frequency counter; generator for mains frequency with phase shifter
Front view, mechanical parts
Top view
Bottom view
1
Unit Unit 4 Unit
6
Unit
3
Unit
2
Unit
5
Overall circuit diagram Circuit diagram: units Circuit diagram: units 1,4, Unit
8
2,
3,
8,
parts of unit
5,
parts of
6
1
6
kHz
sine,
3 - 30
(RF center)
Hz
ALLGEMEINES
Einleitung
Technische Daten
Zubehor Funktionsprinzip
VORBEREITUNGSANWEISUNGEN
Sicherheitstechnische Hinweise
Aufstellen
Erden Offnen des Gehauses Netzanschluss
BETRIEBSANLEITUNG
Bedienungselemente und Anschlusse Bedienung und Anwendung
Anwendungsbeispiele
1.
2.
3. Amplitudenmodulation
4.
5.
6.
7.
Blockschaltbild, gesamt Frontansicht
Frequenzmodulation, Kalibrierung der Tragerfrequenz
Wobbeln, mit verschiebbarer Frequenzmarke, Einstellung der Mittenfrequenz Wobbeln, mit verschiebbarem Frequenzmarkenspektrum
Zahler fiir externe Frequenzen; Generator fur 1 kHz sinus, fur 3 - 30
fur Netzfrequenz mit Phasenschieber
Hz
A,
(RF
center)
TABLE DES MATIERES
GENERALITES
Introduction Caracteristiques techniques Accessoires Principe de fonctionnement
INSTALLATION
Consignes de securite Montage
B
la terre
Mise
Demontage de I'appareil
Branchement de I'appareil
MlSE EN SERVICE
Commandes et douilles
Foqctionnement et application Exemples d'application
RAPPEL DES FIGURES
Schema synoptique
Face avant Modulation d'amplitude Modulation de frbquence, reglage de Wobbulation avec marque decalable de frequence, reglage de la frequence centrale Wobbulation avec spectre decalable de reperes de frequence Compteur des frequences externes; genbrateur pour frequence secteur avec dephaseur
la
frequence porteuse
1
kHz
sinus,
(RF
center)
3
-
30
Hz
A,
Operating
manual
Qservice ----- This Document is a complete scan from the Original Tektronix Manual ----- Qservice
TECHNICAL DATA
General information:
On delivery from the factory, the instrument complies with the safety regulations of measuring and control equipment. The information and warnings contained in this instruction manual must be followed
by the user to ensure safe operation and to maintain the instrument in a safe condition.
-
Only data with indicated tolerances or limits are guaranteed; data without tolerances are given only for guidance.
-
All specifications will be met after a warm-up time of 30 min. when keeping the instrument in a constant mounting position.
-
Inaccuracies (absolute or in
SPECIFICATIONS
R
F Generator
Frequency range Ranges
Frequency display
Error of the display
Temperature coefficient of the display Temperature coeffiecient of the frequency
%)
relate to the indicated reference value.
0,l
-
125
0.1
-
0,25
-
0,5
-
1
-
2,5
-
5
-
10
-
25
-
50
-
125
5-digit
LED
3 decimal points; 2
LEDs for dimension
<
O-~/OC
+5 x 1
-
<
1 0-51°c
MHz
O,25
MHz
0,5
MHz
1
MHz
2,5
MHz
5
MHz
10
MHz
25
MHz
50
MHz MHz
display, red, 11 mm high;
typical,
+I
at 23
kHz,
digit
OC
f
MHz
20
OC
1.2.2.
1.2.3.
R
F
Sweep generator
Ranges
wave form
RF
output
Attenuator
.4/.5
MHz
1011 1 36/41 7511 10
semi-rectangular for all RF ranges and all sweep ranges
Connection: BNC connector RF OUT
Impedance: 75 max. output voltage: 50 mV into 75
Frequency response:< 2 2 dB (1 dB typ.)
>
0 3 dB, 40 dB calibrated
MHz MHz MHz
100 dB total
-
80 dB continous
G?
G?
for all RF ranges
1.2.4.
Modulation
Modulation modes unmodulated
amplitude-modulated, AM frequency-modulated, FM
Frequency response
Modulating output MOD OUT
Amplitude modulation u nmodulated AM, internal
AM, external
Frequency modulation
FM,
internal
FM, external
see also table in chapter all RF ranges and all sweep ranges
all RF ranges and all sweep ranges
dB in
dB in
and
75
(A
f)
(
A
f)
1011 1
.4/.5
36/41
/I
10
:
:
sweep ranges
<
2
<
0.2
1
kHz sine, 2 V
resp. external modulating signal at MOD IN
all RF ranges and all sweep ranges all RF ranges and all sweep ranges
Modulation frequency:
Modulation depth: Modulation depth:
Modulation coefficient:
3
dB band width:
Input impedance:
1011 1
Modulation frequency: Sweep
Modulation signal: Sweep Modulation coefficient:
3
dB band width:
Input impedance:
3.2.
and
7511 10
and
I011 I
and
7511 10
1
30
0-100% 200 mV110 20
>10kR
MHz ranges
1
22,5 20
0 - 75 200 mV/&7,5 20
>I0
MHz
MHz ranges MHz ranges
kHz sine
%
Hz
-
20
kHz sine
kHz
Hz
-
60
kHz
Hz
-
60
k
i-2
%
kHz
kHz
kHz
kHz
AM
(3
dB)
1.2.5.
Wobbulation
Ranges, wobbulation width
Frequency response
Wobble frequency, triangle
-
Linearity error Wobble frequency, sine-wave Center frequency Wobbulating output SWEEP OUT
-
Signal
-
Frequency
-
Amplitude
-
Impedance
Range Width
.4/.5
10/11 36/41 7511 10
<
0,2
3 - 30
MHz MHz MHz MHz
dB in
.4/.5
and
Hz, blanking during fly-back
0 - 50 0-'1 0­0- 1
1011 1
MHz ranges
<5%
Hz line frequency, phase variable
50160
adjustable within the full ranges
triangle
3 - 30
Hz
2,5 - 10,5
Vpp
si
ne-wave
50160 2,5 - 10,5
IkR IkR
(A
2
f) kHz MHz
10MHz
MHz
Hz line frequency
Vpp
1.2.6.
Marker generator
prepared by one of the RF SWEEP RANGE buttons (indicator-LED MARKER is illuminated); switched in by button MARKER
OFFION
1
.2.7.
1.2.8.
variable frequency markers fixed frequencies for adjustable Range Marker distance
frequency marker spectrum
Marker Amplitude Output
l
mpedance
Counter
Frequency range
Input voltage
l
nput impedance
Power supply
Reference value Nominal values Frequency range Power consumption
from RF generator, adjusted frequency on the display
.4/.5
MHz
1011
1
MHz
36/41 7511 10
Marker mixing, superposition; (birdy-marker)
2 2
>
PM
50
AC mains
230
11
48 - 63
I8
MHz MHz
VPP loop-through BNC connectors
500
k
i2
5326:
1
-
999.99
mV
I
Ma
V
5 V/230
W
kHz
-
50
V
V selectable by solder links
HZ
10
100
1
100
kHz kHz
MHz
kHz
PM
1
30
1
5326
kHz
mV
MR
-
-
X:
99.999 50
V
MHz
1.2.9.
Environmental conditions
Ambient temperature
Reference value Nominal working range Safe operation temperature range
Limits for storage and transit
Relative humidity
Reference range Nominal working range
Air pressure
Reference value Nominal working range
1013
800
mbar
...
(2
1066
760
mm Hg)
mbar (up to
2200
m height)
Air speed Reference value
Nominal working range
Operating position
normally upright on feet
or
with handle fold down
1.2.10.
1.3.
1.3.1.
1.3.2.
Warm-up time
Cabinet
Protection type (see DIN 40 050) Protection class (see Overall dimensions
-
height
-
width
-
depth
Weight
ACCESSORIES
Standard
Optional
I
EC 348)
30 min.
IP 20
class
1,
protective conductor
140 rnm 310 mm
330 mm
approx. 6.5 kg
Instruction manual
mA
Fuse 250 PM 9537
PM 9075 Coax cable BNC PM 9072 Coax cable BNC +two 4 mrn plugs
delayed
Coax cable with impedance transformer 75
-
BNC 75
a1300
1.4.
1.4.1.
OPERATING PRINCIPLE (FIG.
RF
circuitry, amplitude modulation
The RF Generator produces the high frequency. The RF FREQUENCY RANGE push-button array allows selecting the desired range, while the continuous the exact frequency. Via Switching Stage and Amplifier 1 the RF frequency unmodulated or amplitude-modulated by the internal 1 kHz Oscillator or by extern MOD IN low fre­quency due to the selected push-buttons MODULATION. The amplitude of the RF frequency is stabilized in the control circuit Amplitude with automatic gain control= in the feedback path. The Output Amplifier can be interacted by the triangle the RF-signal is blanked during fly-back. The RF ATTENUATION sets the output continuously from 0 to -80 dB, but the RF attenuator over­more has two fixed stages of -3 dB and -40 dB.
1)
contro! FREQUENCY SETTING determines
is
fed to the Amplitude Modulator passing eihter
Output blankinkstage: when sweeping with the internal
1.4.2.
1.4.3.
Sweep section and frequency modulation
The LF Sweep Generator produces and modulates high frequencies for the sweep ranges .4/.5, 10/11, 36/41, 7511 10 MHz, selected by push-buttons RF SWEEP RANGE. The waveform is semi-rectangular. The carrier for the frequency modulation and the center frequency for the wobbulating ranges respec­tively are set in Frequency Selection, activated by RF SWEEP RANGE just mentioned and coarse and fine adjusted by the double continuous control RF CENTER.
Pressed button internal or with external signal via MOD IN input socket. If one of the RF SWEEP RANGE buttons
frequency
Due to the different frequency ranges the maximum sweep width is adapted by RF SWEEP RANGE. Control The sweeping or wobbulating signal and the signal for X-deflexion of an indicator or oscilloscope at the MODISWEEP OUT socket can be switched off by push-button SWEEP OFFION. In this case the modu-
lating signal
Frequency marker
The Marker Mixer superimposes the frequency of the RF Generator to the swept frequency of the RF Sweep Generator. The low frequency beat the OUT-Y-IN socket for the Y-channel of an indicator (oscilloscope). Each frequency of the RF Gene­rator can be used for frequency marker, Pulling the button MARKER AMPL generates fixed markers with many harmonics. The fundamental wave of the fixed marker due to the sweep range When using triangular sweep mode the square wave output of the LF Sweep Generator blanks the fre­quency markers in the Marker blanking-during fly-back.
AMIFM activates frequency modulation of the ranges 1011 1 or 7511 10 MHz with 1 kHz
is
pressed, the frequency modulated or wobbulated high
is
fed via the Switching Stage to the main RF output path.
RF
WIDTH reduces the width.
is
available at the output.
is
filtered in the Band-pass Filter Amplifier 3 and fed to
i.
e.
"travelling marker".
is
selected by RF SWEEP RANGE. So a marker spectrum with suited distance
is
generated.
1.4.4.
1.4.5.
Display circuitry
is
The frequency of the RF-Generator Counter Decoder Driver which
is
for the counter, measuring period represents the frequency which is multiplex-displayed on the 5-digit display. Push-button COUNTER EXT enables the display circuitry working as normal counter. Amplifier the signal at the COUNTER IN socket directly to the counter, decoder and driver.
Power supply
The -power
sinusoidal wobbulating voltage.
changed by the chosen frequency range. The stage of the counter at the end of one
suppb. provides the stabilized DC voltages of
divided depending on the selected frequency range and fed to the
is
controlled by the Time Base. The Time base, i.
+5
V, +I2 V, -12 V and +27 V, and the
e.
one measuring period
5
feeds
INSTALLATION
SAFETY REGULATIONS
Upon delivery, the instrument complies with the required safety regulations. To maintain this condi-
it
is
tion and to ensure safe operation,
recommended to follow the instructions below.
2.1.1.
2.1.2.
Before connecting
Mains voltage Check whether the instrument
Protection
is
This instrument
mains cable provides earth connection. Outside specially protected rooms, the mains plug must be con­nected only to sockets with earthed contact.
It
is
not allowed to interrupt the earth connection inside or outside the instrument.
Maintenance and repair
Failure and excessive stress If the instrument This is the case when the instrument
-
shows physical damage
-
does not function anymore
-
is
stressed beyond the tolerable limits (e. g. during storage and transportation)
Dismantling the instrument When removing covers or other parts by means or tools, live parts or terminals could be exposed. Before
opening the instrument, disconnect it from all power sources.
If the open live instrument needs calibration, maintenance or trained personnel being aware of the risks. After disconnection from in the instrument may remain charged for some seconds, observe the circuit diagrams.
protected according to class I (protective earth) of the
is
suspected of being unsafe, take
is
adapted to the nominal mains voltage.
it
out of operation permanently.
a
repair,
l
EC
348
or VDE
it
must be performed only by
all
power sources, the capacitors
041
1.
The
Fuses Only use the specified fuses.
Repair, Replacing parts
is
Repairs must be made by trained personnel. Ensure that the construction of the instrument to the detriment of safety. Above all, leakage paths, air gaps and insulation layers must not be reduced.
When replacing, use only original parts. Other spare parts are only acceptable when the safety precau­tions for the instrument are not impaired.
not altered
MOUNTING
The instrument may be used in any desired position. With the handle fold down, the instrument may be used in sloping position; for this purpose press the buttons A of the handle (Fig. 2). Do not position the
instrument on any surface which produces or radiates heat, or in direct sunlight.
EARTHING
Before switching on, the instrument must The mains cable fixed to the instrument includes earth contacts of the plug. Thus, when connected to an earthed mains socket, the cabinet of the instru-
is
ment WARNING: Connect the mains cable plug only to
The circuit earth potential applied to the external contacts of BNC sockets The external contacts of the BNC sockets must not be used to conpect a protective conductor.
consequently connected to the protective earth.
tection must not be made ineffective, protection!
be
earthed in conformity with the local safety regulations.
a
protective conductor, which is connected to the
a
socket with protective earth contacts. This pro-
e.
g. by using an extension cable without earth
is
connected to the cabinet.
DISMANTLING THE INSTRUMENT
-
Unplug the mains connector
-
Fold up the handle to the top. For this push the buttons A (Fig.
-
Loosen the central screw at the rear
-
Remove the lead-through of the mains cable from the cabinet
-
Dismantle the cabinet
2)
MAINS CONNECTION
The instrument must be connected only to an AC supply. On delivery the instrument
Before mains connection, ensure that the local mains voltage ranges within the
indicated on the plate at the rear of the instrument.
is
If the instrument
-
Unplug the mains connector
-
Dismantle the instrument, see
-
Resolder links on the mains transformer in accordance with the stick-on connection diagram. See
also below.
to be used on
11
2.4.
5
V
supply, proceed as follows:
is
set to 230
set
mains voltage range
V.
-
Insert the supplied fuse
-
Change the mains voltage plate at the rear of the instrument in accordance with the mains voltage selected. This plate for
-
Close the instrument
Mains connection must
is
instrument
connected to mains socket with protective earth contact (see para. 2.3.).
250
mA delayed into the fuse holder instead of the one built-in
11
5
V
is
inserted into a plastic cover
be
made in accordance with the local safety regulations. This implies that the
3.
OPERATING INSTRUCTIONS
3.1.
3.1 .I.
3.1
-2.
CONTROLS
Legend Position Function
Frequency
RF FREQUENCYRANGE
.I
-
FREQUENCY SETTING RF ATTENUATION
0/30/40 dB
RF ATTENUATION
-
80 dB
0
RF OUT Display
kHz, MHz
Modulation
MODULATION
C
...
-
125 MHz
AND
SOCKETS (FIG.
2)
801.2 to
801.10
802 pushbuttons; change-over contacts
pushbuttons for selecting the frequency range
knob for continuous frequency adjustment rotary switch for setting the fixed attenuation
knob for continuous attenuation adjustment
BNC output socket for RF signal 5-digit LED frequency display;
2 LEDs for dimension
not pressed
C
OFFION
AM/FM
I
NT/E XT MOD IN MODISWEEP OUT SWEEP
RF CENTER
802.1 unmodulated modulated
802.2 amplitude-modulated frequency-modulated
802.3 internal 816 81 5 603
BNC input socket for external modulation voltage BNC output socket for modulation signal
dual-knob (coarse, fine) for continuous carrier adjustment
pressed
external
3.1.3.
Sweep
RF SWEEP RANGE
.4/.5 MHz
10/11 MHz
36/41 MHz
7511 10 MHz SWEEP
OFFION
SWEEP
A
N
pushbuttons; change-over contacts
not pressed
pressed
802
802.7
mod.
802.8 frequency
802.9
802.1 0 frequency mod. prepared FM (band 2)
802.5
802.6 triangular wobbling wobbling
prepared
AM -IF
-
IF
FM
TV
-
IF
wobbling
at
line frequency
Legend Position
Function
3.1.4.
SWEEP RF CENTER
SWEEP
RF WIDTH
SWEEP LF FREQUENCY PHASE
SWEEP
LF AMPLITUDE
SWEEP OUT
Frequency markers
MARKER OFFION
MARKER MARKER AMPL PULL FOR FIXED MARKERS
IN-Y-OUT
605 605 813,814
dual-knob (coarse, fine) for continuous adjustment of the centre frequency of the wobbling range
knob for continuous adjustment of the wobbling width
knob for continuous frequency adjustment on trian­gular wobbling or phase adjustment on wobbling at line frequency
knob for continuous adjustment of the wobbling voltage
BNC output socket for the wobble signal
pushbutton for operation with frequency markers
LED for operation with markers knob for continuous adjustment of marker amplitude
pull switch for adding fixed frequencies
2
BNC sockets:
-
output socket for marker signal
-
mixing device for superposition of test object output signal with marker signal
3.1.5.
3.1.6. 1
3.1.7.
3.1.8.
Counter
COUNTER EXT COUNTER IN
kHz sine-wave generator
MODISWEEP OUT
Triangle generator
SWEEP OUT
LF AMPLITUDE
Power supply
POWER ON o @OFF
801
81
2
81 5
81 5 602
851
.I
commutator for frequency counter mode BNC counter input socket
BNC output socket for 1 kHz sine wave
BNC output socket for triangle signal of sweep generator
knob for continuous amplitude adjustment
mains switch: white dot for ON position
OPERATION AND APPLICATION
Mode of operation
+
RF signal generator, unmodulated
-
Betriebsarten - Mode d'operation
OFF
0
Fig. 7
N
0
M
,
C
ULATIC
AM
FM o
--
INT
E XT
WOBBULATION
.
AARKER requency
IFF,
I
N
e
iENER. carrier frequency
AMPL,
PULL
marker distance
10 kHz
100 kHz
1
MHz
100 kHz
All push-buttons are off only contains the controls, function blocks, inputs and outputs which take active part of the applications.
RF signal generator, amplitude modulated
As 3.2.1., button MODULATION OFFION pressed. The set carrier depth.
As 3.2.2.. button MODULATION INIEXT pressed. The set carrier in via MOD IN. At socket MOD OUT the external modulating voltage
RF signal generator, frequency modulated
All push-buttons are off except the concerning one of the RF SWEEP RANGE 1011 1 or 7511 10 and the buttons for modulation OFFION and AMIFM (fig. modulated by 1 kHz.
As 3.2.3. and button MODULATION INIEXT pressed. The set carrier NF voltage, fed in via MOD IN. At the socket MOD OUT the NF voltage
Note!
Adjustment of the carrier frequency see fig.
exceptthe concerning one of the RF FREQUENCY RANGE (fig. 3). The figure
is
modulated by 1 kHz to 30
is
modulated by the NF voltage fed
is
available.
4).
The carrier, fixed or to
is
frequency modulated by the
is
available.
4
be
set , is frequency
%
3.2.4.
Wobbulator with variable frequency marker
All push-buttons are off except the concerning one of the RF SWEEP RANGE, SWEEP OFFION and MARKER OFFION (fig. 5).
RANGE and set by RF CENTER. The sweep width
by control RF WIDTH.
The sweep frequency of the ALF signal fier and marker mixer are blanked. During sweep the marked band-pass can be seen on an indicator. The altitude of the marker
It
is
swept about the center frequency, which
is
pre-determined due to the range and can be varied
is
set by LF FREQUENCY. During fly-back the output ampli-
is
set by the MARKER AMPL control.
is
chosen by button RF SWEEP
3.2.5.
3.2.6.
3.2.6.1.
3.2.7.
3.2.8.
As in the first chapter 3.2.4. In addition button SWEEP~l~pressed.
(sine). The output and the marker signal are
are identically covered by the PHASE control. The X-channel of the indicator
output. The scale-factor
Wobbulator with travelling marker and coupled marker spectrum
According to 3.3.4. with additionally pulled turn-knob MARKER
Frequency counter
All push-buttons off except COUNTER EXT (fig. 7).
In this mode of operation the center frequency of the RF sweep generator can directly
in range .4/.5 and adjusted by means of button CENTER. For this connect the sockets RF OUT and
COUNTER IN and push the button .4/.5.
1
kHz
sine-wave generator
All push-buttons off except MODULATION OFFION; the signal
(fig. 7).
Triangle generator
All push-buttons off except SWEEP OFFION and one of the buttons RF SWEEP RANGE. The frequency
is
set by LF FREQUENCY, the amplitude by LF AMPLITUDE. The signal
7).
(fig.
is
set by LF AMPLITUDE; see 3.3.6.3.
not
blanked during fly-back. Sweep and fly-back curves
It
is
wobbulated at line frequency
is
fed in via SWEEP OUT
AMPL.
(fig. 6)
be
measured
is
fed to the MODISWEEP OUT socket
is
available at SWEEP OUT
APPLICATION'EXAMPLES
General measuring principle
is
Due to the fact that the output voltage
vity can be conveniently measured.
by keeping the output level constant, or the method of "signal tracing". The choice depends mainly
on the importance either of the non-reactive signal supply or of the signal decoupling with low detuning.
is
The first method
subject to matching problems, the second to detuning phenomena.
It
accurate and stable over a large range, gain and sensiti-
is
possible to apply the method of "continuous signal supply"
>
PM
5326
Fig. 3.3-1 Continuous signal supply
I
PM
5326
C
Fig. 3.3-2 Signal tracing
>
Test object
4
-
L--J
Test o
I
1
I I
I
bj
ec t
?
I
I
I
A
-,A
>
Indicator
-
r
lndicator
'r
I
i
I
Usually the transmission characteristic of a selective
point.
L
PM
5326
Fig. 3.3-3 Static measuring method
f
RF
D
Test object
test
object
>
_j
is
measured statically,
?
Indicator
i.e.
point by
The static method gives very reliable results, but takes much time. As mostly only the shape must be
determined and not the absolute values of the transmission characteristic, the dynamic method (wobb­ling) is generally preferred.
PM
Fig.
5326
3.3-4
Dynamic measuring method
Oscilloscope
3.3.2.
3.3.3.
Mains connection, general Connect the RF-generator PM
should be connected to mains via an isolating transformer. Only one this transformer at the same time. When measuring all-mains receivers or TV former must be used. Correctly connect the chassis of the of the test setup.
Connection of
It
is
recommended to observe always the checking and adjusting procedures given by the manufacturer of the test object (see fig. The
test
are optional:
9072:
PM PM
9075:
In the FM range, the impedance transformer PM
to the input impedance of the
In the AM range, a dummy aerial according to fig.
an AM aerial.
RF
generator
object may be connected to the RF generator via the cables mentioned below. These cables
cable BNC - 4mm plugs cable BNC - BNC
5326
3.3-20).
test
object;
according to para.
9537
75R /300n.
2.5.
of the Instruction Manual. The
test
object may be connected to
sets,
an isolating trans-
test
object to earth. Avoid double earthing
adapts the output impedance of the generator
3.3-5
may be used to simulate the impedance of
test
object
Fig.
3.3-5
Dummy aerial for AM range
Due to the low input impedance of a modern AM receiver, an isolating capacitor of 30 nF must connected to the PM 9072, for example.
its
IF input. This capacitor must be mounted directly at the end of the cable, as with
I::
---
be
Fig. 3.3-6
Unit
AM-IF
FM-IF
FM-Tuner
Selectivity
For defined signal decoupling with low detuning and damping, a probe with damped resonant circuit can be used as attenuator. The coil of this circuit the resonant voltage downward during signal decoupling. The L/C ratio must be optimized for AM-
IF and FM-IF with particular regard to coil losses.
For application in the AM-IF range, for example, the capacitive detuning the trimmer and by tapping the medium and high-ohmic potentials of the test object.
Isolating capacitor for low-ohmic signal.supply
C
via
33 nF
10 nF direct direct
20 kHz 200 kHz 200 kHz 200 kHz
is
tapped
A
f
fwob
Hz
50 50 Hz 50 Hz
IOHZA
at
the ratio of 1011, thus transforming
is
eliminated by means of
3.3.4.
Fig. 3.3-7
Automatic gain control To prevent incorrect measurements,
the test object. Measuring results obtained at too high levels without suppression of AGC, are subject to considerable errors. This applies to wobbling,
Probe with selective voltage divider
AGC
of test object
it
is
necessary to test the efficiency and set-in level of AGC of
as
well as to static methods.
It
is
common practice to adequately fix the sliding DC voltage of AGC to a constant DC voltage from
be
a low-ohmic source. This can
if the controlling DC voltage of the
In case of conductive hum-pickup, it tap the voltage by means of a potentiometer circuit becomes more low-ohmic with moderate battery load, if the potentiometer
is
followed by a transistor ermitter-follower stage.
The connection point and the voltage level to be set are given in the checking and adjusting procedures of the test object. Receivers with suppressed (delayed) control set-in point produce acceptable measur-
ing values, when working below the set-in point during measurement, so that the control is not effective.
achieved by an adjustable DC supply
test
object
is
related only to the chassis without being isolated.
is
recommended to use a dry battery or an accumulator and to
a
potentiometer connected in parallel to the battery. The output of such
(e.
g.
PE
1535 or
PE
15371,
3.3.5.
3.3.5.1.
)I@---l
Type and connection of indicator The following indicators can
pV- or mV-meters, broadband voltmeters, oscilloscopes, wobble indicators and x/y recorders.
Connection to With supply of modulated signals,
are replaced by resistors. Adjust the operating controls: volume to medium level, bass control to maximum, treble control to maximum, bandwidth to narrow. With several
LF
output
LF
channels, connect the indicator to the bass channel.
(eg
PM
be
used: multi-purpose instruments, calibrated signal tracers, selective
it
is
possible to connect indicators to
2503)
LF
outputs. The loudspeakers
rl
Indicator
Fig. 3.3-8
Connecting indicator to
LF
output
3.3.5.2.
Multi-purpose instruments
can be used as indicators of rectified currents of demodulators in AM and FM receivers and as limiters
with FM receivers and TV sets.
3.3.5.3.
Fig. 3.3-9
For determining the gain of the IF stage
in AM receivers, the probe (ratio of described before,
Connection to AM, FM demodulators or FM limiter
HF
signal must be decoupled. This can be achieved by means of a voltage divider
10
:
1,
for example) with low detuning and damping. The resonant circuit probe,
is
also suited.
Fig. 3.3-10
Determination of gain of an AM stage
3.3.5.4.
Adjusting overcritical coupled band filters The mostly overcritical coupled band filters in the FM-.IF amplifier must be damped and adjusted
as
short
as
alternately. The connection wires of the damping resistor should be
possible.
Indicator
3.3.5.5.
Fig. 3.3-1 1
Adjusting overcritical coupled
IF band filters
Repeat the adjustment of a band filter several times.
Symmetry of a ratio detector
The S-shaped demodulator characteristic (fig. 3.3-17) should be linear and symmetric to the zero-axis crossing with normal control. For determining the symmetry,
.
detector in amplitude limitation
The rectified voltage
at
the limiter capacitor C2 is halved in the vol-
it is convenient to adjust the
ratio
age divider and is symmetricalwith refence to the LF demodulator output (fig. 3.3-12). For recording
last
the s-shaped demodulator characteristic, supply the signal to the base of the
R
1
U
n
R
6
10k
Y
n
IF stage.
3.3.6.
3.3.6.1.
a
Fig. 3.3-12
Adjusting the symmetry of
ratio detector
Examples of wobbling
Test setup for checking and adjusting an
see
fig. 3.3-13. Examples of oscillograms are shown in figs. 5 and
FM
receiver
6.
The centre frequency in the FM-IF
The X-channels of wobble indicators,
oscilloscopes, special wobble displays or X
linearity errors occur in X-direction, particularly with slow wobbulating frequencies.
Finite lower limit frequencies in the Y-channel cause pulse droops due to suppression of the DC com­ponents. In this way, an error is simulated, which the Y-channel has less effect, as the Y-signal frequency. The oscillograms show that the leading and trailing edges are not very steep.
The non-linearity of an X-channel with finite lower limit frequency sine-waves at mains frequency.
As the edges of the wobbling sine-signal are not linear, wobbling must be symmetric to the zero-axis
crossing to obtain a deflection synchronous and in phase with the sinusoidal frequency variation. This
is the case, when the sweep-flyback
AGC
of wobbled object
For suppression of AGC of the wobbled object, see para. are suited for this purpose.
Frequency marks
'
For marking mixed and the modulationproduct is selected by means of a narrow-band LF amplifier. The frequency marks are produced by amplitude modulation, fig.
a frequency of the transmission characteristics, the frequencies RF and RF sweep are
is
-
Y high-speed recorders must be DC-coupled. Otherwise,
is
actually not present. The upper limit frequency of
is
decoupled after the demodulator and is therefore at low
is
reducible, when wobbled with
made coincident by means of control PHASE.
3.3.4.
The DC supplies PE
3.3-14.
1535
or PE
1537
This frequency mark is adjustable over the transmission characteristic by varying the frequency of
3.3-14
the RF generator, fig.
and fig.
5.
f
min.
CENTER
A
-
x
-
tal
controlled
~RF
-
A
f
max
,
*
adj. Marker
f
Fig.
3.3-14
The frequency mark signal Y-signal. The output signal of the test object is active at the Y-input of the wobble indicator via the loop-through IN-Y-OUT and produces a frequency mark at the required point of the transmission characteristics, fig.
Adjustable frequency marks
is
available at the BNC connector IN-Y-OUT to be superimposed to the
3.3-1
6.
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